1. Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly to a color cathode-ray tube which has an optimum funnel structure so that it has a slim tube structure while reducing stress caused by its internal vacuum pressure.
2. Description of the Related Art
FIG. 1a is a partially-broken side view illustrating the structure of a general color cathode-ray tube.
Such a color cathode-ray tube is used as an essential element for displaying images in an image display unit such as a television receiver or a computer monitor. Referring to FIG. 1a, the color cathode-ray tube includes a panel 1 constituting a front part of the cathode-ray tube, and a funnel 2 extending rearward from the panel 1.
The color cathode-ray tube also includes a fluorescent film (screen) 4 coated over the inner surfaces of the panel 1 and funnel 2 to serve as a desired luminescent element, an electron gun fitted in a neck portion 13 of the funnel 2 and adapted to emit electron beams 6 for causing the fluorescent surface 4 to emit light, a shadow mask 3 for performing color selection for causing desired portions of the fluorescent film 4 to emit light, a frame including a main frame 7 adapted to apply tension to the shadow mask 3, and a sub frame 8 adapted to support the main frame, springs 9 mounted to respective side portions of the main frame 7 to allow the frame to be coupled to the panel 1, an inner shield 10 welded to the sub frame 8 and adapted to shield an external earth magnetic field, and a reinforcing band 12 fitted around the panel 1 and adapted to protect the panel 1 from external impact.
A deflection yoke 5 and magnets 11 of 2, 4, and 6 poles are arranged around the neck portion 13 of the funnel 2. The deflection yoke 5 serves to deflect electron beams 6 emitted from the electron gun (not shown) in upward, downward, leftward, and rightward directions. The magnets 11 serve to correct the travel paths of the emitted electron beams 6 so as to cause those electron beams 6 to accurately strike onto desired portions of the fluorescent film 4, thereby preventing a degradation in color purity.
The manufacturing process of the general color cathode-ray tube having the above described configuration mainly involves a pre-process and a post-process. The pre-process is a process for coating a fluorescent film over the inner surface of the panel. The post-process involves various processes.
That is, the panel coated with the fluorescent film and mounted with a mask assembly therein, and the funnel coated with frit at a seal surface thereof are subjected to a sealing process in a furnace maintained at high temperature so that they are coupled to each other. The electron gun is fitted in the neck portion of the funnel in an encapsulating process. A vacuum is formed in the interior of the cathode-ray tube in accordance with an air exhaust process. The cathode-ray tube is then sealed.
When the cathode-ray tube is in a vacuum state, its panel and funnel are subjected to high tensile stress and high compressive stress.
To this end, a reinforcing process is carried out to attach the reinforcing band to the panel for dispersion of high stress exerted on the front surface of the panel. Thus, the manufacture of the cathode-ray tube is completed.
Meanwhile, although digitalization of cathode-ray tubes is important, slimness of those cathode-ray tubes is also important in association with the securing of a redundant space.
Where cathode-ray tubes have a slim structure, their glass portions are subjected to vacuum stress increased correspondingly to a reduction in volume caused by the slimness, because the vacuum pressure is constant in spite of the volume reduction.
Furthermore, in such a slim cathode-ray tube, formation of high stress mainly occurs at the funnel portion having a relatively small thickness, rather than at the panel. In particular, the seal line portion of the cathode-ray tube may be easily damaged in a thermal process because high tensile stress is present at that seal line portion.
Methods for reducing the overall length of a cathode-ray tube have also been proposed. Such methods include a method for reducing the overall length of the panel, and a method for reducing the overall length of the funnel body. The method for reducing the overall length of the funnel body may be more preferable.
Where the overall length of the panel is reduced under the condition in which the funnel has a relatively thin structure, an undesirable result may occur in association with formation of high tensile stress at the seal line portion due to the vacuum pressure generated in the air exhaust process. Furthermore, it may be impossible to provide a sufficient space for the clamping of the band. As a result, a degradation in the effectiveness of the band may occur due to an insufficient clamping tension of the band.
FIG. 3 shows distribution of stress applied to the panel and funnel glass under the condition in which a vacuum is formed in the interior of the cathode-ray tube in accordance with an air exhaust process. In FIG. 3, the phantom line represents compressive stress, whereas the solid line represents tensile stress.
Cracks may be formed when glass is subjected to external impact. In this case, tensile stress applied to the surface of the glass accelerates propagation of cracks. Where the applied tensile stress is excessively high, the glass may be broken. On the other hand, compressive stress serves to prevent propagation of cracks.
Referring to FIG. 3, the central portion of the panel, the central portion of a skirt extending from the peripheral edge of the panel, and the central portion of the funnel are relatively resistant to impact because they are subjected to compressive stress, whereas the corner portions and seal line portion of the panel are sensitive to impact because they are subjected to tensile stress.
For reducing or coping with high tensile stress generated at the glass, various methods have been proposed in association with the panel. For example, a method using a reinforcing band, and a method using a reinforced glass having an increased stiffness in accordance with a thermal treatment of the glass, and a method using a film to be attached to the surface of the panel have been proposed. However, the reinforcing band exhibits an insufficient effect where it is applied to the funnel. Furthermore, there has been no case in which reinforced glass is used for the funnel.
Accordingly, a technique to secure desired resistance to impact while reducing stress is required for the funnel.